1. Field of the Invention:
This invention relates to a vehicle transmission and more particularly to a continuously variable transmission (which will be referred to herein as a "CVT") for transmitting power at variable speed by means of belts running in pulleys of variable groove width.
2. Description of the Prior Art:
By adopting the CVT as a vehicle transmission, there have been made in the prior art attempts to facilitate the gear shifting or gear changing operation, to improve acceleration, and to reduce fuel consumption, by selecting such a load or such a speed of rotation at vehicle cruising speed as to use substantially the highest thermal efficiency of the engine of the vehicle. One example is known in which such an attempt has succeeded in an automobile having a small engine.
However, most existing CVTs use the known system in which power is transmitted through point contact. Increase of the contact force with a view to increasing power transmission capacity is limited by the allowable Hertz stress of a material, so that CVTs are not generally suitable for transmission of high power. In another known system, power is transmitted by line contact instead of by point contact. However, since the transmission to be theoretically carried out by point contact is conducted through line contact, slipping occurs in the segment other than the portion where the point contact theoretically dominates. As a result, friction loss is increased so as not only to reduce transmission efficiency substantially, but to generate heat through the lost energy and so reduce the reliability of the system. In addition it is the current practice that apparatus for transmitting a power as much as several hundred horse power is of large size, so that it is difficult to find a market because of its heavy weight or high price.